1. Field of the Invention
The present invention relates to an electronic device provided with a fan motor. In particular, the present invention relates to the configuration of an electronic device, in which a fan motor is attached to the top portion of a casing containing electronic components.
2. Description of the Related Art
An electronic device used for, for example, a numerical control device of a machine can be provided with a fan motor for cooling, for example, a control board or electronic components contained in a casing of the electronic device. When such an electronic device is used for a long period of time in a machine factory, moisture or cutting fluid mist contained in air within the factory accumulates on the fan motor. When the fan motor is disposed on the top portion of the casing of the electronic device, the moisture or cutting fluid mist, which has accumulated on the fan motor, turns into droplets and then drops to the inside of the casing, and thereafter, adheres to the control board or the electronic components within the casing. This may cause a short circuit or deterioration of the electronic components in some cases.
Japanese Patent Application Laid-open No. 2007-48946 proposes the structure of an electronic device, in which a fan motor is disposed at the upper side of a ventilation hole formed in the upper wall of a casing. In the structure, a housing for the fan motor is attached to the top face of the upper wall of the casing via a clearance.
FIG. 20 is a top view of the electronic device disclosed in Japanese Patent Application Laid-open No. 2007-48946. FIG. 21 is a sectional view taken along line X-X′ in FIG. 20. FIG. 21 also includes an enlarged view of an encircled portion K. FIG. 22 is a view of the inside of the electronic device shown in FIG. 21 when viewed from the direction designated by an arrow Y.
As shown in FIGS. 20 to 22, the electronic device disclosed in Japanese Patent Application Laid-open No. 2007-48946 is provided with a casing 103 containing a control board 102 on which an electronic component 101 is mounted, and a fan motor 104 for cooling the electronic component 101 and the control board 102 within the casing 103. The fan motor 104 has a housing 105. The fan motor 104 is disposed on the upper wall of the casing 103 via the housing 105. A ventilation hole 106, through which an airflow generated by the fan motor 104 passes, is formed in the upper wall of the casing 103.
Further, in the electronic device disclosed in Japanese Patent Application Laid-open No. 2007-48946, as shown in FIG. 21, the housing 105 of the fan motor 104 is attached to the upper wall of the casing 103 via a clearance 107. This structure causes most of fluid adhering to the fan motor 104 to move to the inner surface of the housing 105 due to a centrifugal force of the fan motor 104 when the fan motor 104 rotates. Consequently, the fluid flows, as designated by an arrow S in FIG. 21, from the inner surface of the housing 105 to the outer surface of the casing 103 through the clearance 107.
However, the structure of the electronic device disclosed in, for example, Japanese Patent Application Laid-open No. 2007-48946 (see FIGS. 20 to 22) has a problem that will be described below.
When the fan motor 104 stops, as designated by an arrow T in FIG. 21, the fluid remaining on vanes of the fan motor 104 collects at a lowermost point 108 of each vane as time passes. Consequently, a droplet grows at the lowermost point 108 of the vane, and, as designated by an arrow U in FIG. 21, the droplet drops to the inside of the casing 103 and then adheres to the control board 102 or the electronic component 101. Thus, even in the structure of the electronic device disclosed in Japanese Patent Application Laid-open No. 2007-48946, a short circuit or deterioration of the electronic component 101 may arise in some cases.